In the packaging of various commodities, it has become desirable to provide some indication as to whether the contents had been tampered with. In such packages, one common expedient has been to form a ring on the closure of the container which is broken or severed when attempts are made to remove the closure. In one type of such package, that is shown for example in U.S. Pat. Nos. 3,329,290, 3,784,041, 4,322,009 and 4,343,308, the closure includes an integral pilfer ring that snaps over an annular bead on the container and is fractured or severed from the closure when the closure is removed. As shown in U.S. Pat. No. 4,322,009, the pilfer ring is connected to the remainder of the skirt by bridge portions formed in the skirt after molding of the closure by slitting the skirt circumferentially. In U.S. Pat. No. 4,343,308, an attempt is made to control the fracture of the pilfer ring by molding the closure with a groove on the periphery of the skirt in order to accurately control the thickness of the skirt from about 0.003 inches to 0.005 inches.
Although such tamper indicating packages are satisfactory for the purpose of indicating tampering, the presence of the tamper or pilfer ring raises problems during the application of the closure to the container. In the process of applying the closure, the pilfer band is subjected to a series of stresses which tend to break the band away from the remainder of the closure in which case the tamper indicating feature of the package will be lost. More specifically, as the closure is threaded onto the container, the pilfer band bridge portions and skirt are subjected to a compressive action against the annular bead on the container and thereafter a flexing of the bridge portions of the pilfer band by displacement radially outwardly over the annular bead and finally by snapping action to an axial stress. If the bridge portions are made stronger to prevent damage, then the closure is apt to be more difficult to remove or the pilfer band will not function by breaking away from the skirt, or both of these could result.
Accordingly, among the objectives of the present invention are to provide a tamper indicating package which includes a closure that can be applied to the container without damage and yet can be readily removed by the user during which removal the pilfer ring functions to indicate that the closure has been removed or possibly tampered with.
In accordance with the invention, an annular groove is formed into the closure in the area of the bridge portions by deforming the area radially after the closure is molded and prior to slitting to form the bridge portions. This displaces the material axially lengthening the skirt and at the same time making the area of the skirt thinner but stressed such that it will more readily withstand the stresses of applying the closure to the container.